LSM: syscalls for current process attributes

Create a system call lsm_get_self_attr() to provide the security
module maintained attributes of the current process.
Create a system call lsm_set_self_attr() to set a security
module maintained attribute of the current process.
Historically these attributes have been exposed to user space via
entries in procfs under /proc/self/attr.

The attribute value is provided in a lsm_ctx structure. The structure
identifies the size of the attribute, and the attribute value. The format
of the attribute value is defined by the security module. A flags field
is included for LSM specific information. It is currently unused and must
be 0. The total size of the data, including the lsm_ctx structure and any
padding, is maintained as well.

struct lsm_ctx {
        __u64 id;
        __u64 flags;
        __u64 len;
        __u64 ctx_len;
        __u8 ctx[];
};

Two new LSM hooks are used to interface with the LSMs.
security_getselfattr() collects the lsm_ctx values from the
LSMs that support the hook, accounting for space requirements.
security_setselfattr() identifies which LSM the attribute is
intended for and passes it along.

Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Serge Hallyn <serge@hallyn.com>
Reviewed-by: John Johansen <john.johansen@canonical.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>

5 files changed, 65 insertions, 0 deletions

diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
index ff217a5ce552..c925a0d26edf 100644
--- a/include/linux/lsm_hook_defs.h
+++ b/include/linux/lsm_hook_defs.h
@@ -262,6 +262,10 @@ LSM_HOOK(int, 0, sem_semop, struct kern_ipc_perm *perm, struct sembuf *sops,
 LSM_HOOK(int, 0, netlink_send, struct sock *sk, struct sk_buff *skb)
 LSM_HOOK(void, LSM_RET_VOID, d_instantiate, struct dentry *dentry,
 	 struct inode *inode)
+LSM_HOOK(int, -EOPNOTSUPP, getselfattr, unsigned int attr,
+	 struct lsm_ctx __user *ctx, size_t *size, u32 flags)
+LSM_HOOK(int, -EOPNOTSUPP, setselfattr, unsigned int attr,
+	 struct lsm_ctx *ctx, size_t size, u32 flags)
 LSM_HOOK(int, -EINVAL, getprocattr, struct task_struct *p, const char *name,
 	 char **value)
 LSM_HOOK(int, -EINVAL, setprocattr, const char *name, void *value, size_t size)
diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index 7f0adb33caaa..a2ade0ffe9e7 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -25,6 +25,7 @@
 #ifndef __LINUX_LSM_HOOKS_H
 #define __LINUX_LSM_HOOKS_H
 
+#include <uapi/linux/lsm.h>
 #include <linux/security.h>
 #include <linux/init.h>
 #include <linux/rculist.h>
diff --git a/include/linux/security.h b/include/linux/security.h
index c81bca77f4f2..dd1fe487385d 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -60,6 +60,7 @@ struct fs_parameter;
 enum fs_value_type;
 struct watch;
 struct watch_notification;
+struct lsm_ctx;
 
 /* Default (no) options for the capable function */
 #define CAP_OPT_NONE 0x0
@@ -472,6 +473,10 @@ int security_sem_semctl(struct kern_ipc_perm *sma, int cmd);
 int security_sem_semop(struct kern_ipc_perm *sma, struct sembuf *sops,
 			unsigned nsops, int alter);
 void security_d_instantiate(struct dentry *dentry, struct inode *inode);
+int security_getselfattr(unsigned int attr, struct lsm_ctx __user *ctx,
+			 size_t __user *size, u32 flags);
+int security_setselfattr(unsigned int attr, struct lsm_ctx __user *ctx,
+			 size_t size, u32 flags);
 int security_getprocattr(struct task_struct *p, int lsmid, const char *name,
 			 char **value);
 int security_setprocattr(int lsmid, const char *name, void *value, size_t size);
@@ -1338,6 +1343,20 @@ static inline void security_d_instantiate(struct dentry *dentry,
 					  struct inode *inode)
 { }
 
+static inline int security_getselfattr(unsigned int attr,
+				       struct lsm_ctx __user *ctx,
+				       size_t __user *size, u32 flags)
+{
+	return -EOPNOTSUPP;
+}
+
+static inline int security_setselfattr(unsigned int attr,
+				       struct lsm_ctx __user *ctx,
+				       size_t size, u32 flags)
+{
+	return -EOPNOTSUPP;
+}
+
 static inline int security_getprocattr(struct task_struct *p, int lsmid,
 				       const char *name, char **value)
 {
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index fd9d12de7e92..4e1e56a24f1e 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -71,6 +71,7 @@ struct clone_args;
 struct open_how;
 struct mount_attr;
 struct landlock_ruleset_attr;
+struct lsm_ctx;
 enum landlock_rule_type;
 struct cachestat_range;
 struct cachestat;
@@ -949,6 +950,10 @@ asmlinkage long sys_cachestat(unsigned int fd,
 		struct cachestat_range __user *cstat_range,
 		struct cachestat __user *cstat, unsigned int flags);
 asmlinkage long sys_map_shadow_stack(unsigned long addr, unsigned long size, unsigned int flags);
+asmlinkage long sys_lsm_get_self_attr(unsigned int attr, struct lsm_ctx *ctx,
+				      size_t *size, __u32 flags);
+asmlinkage long sys_lsm_set_self_attr(unsigned int attr, struct lsm_ctx *ctx,
+				      size_t size, __u32 flags);
 
 /*
  * Architecture-specific system calls
diff --git a/include/uapi/linux/lsm.h b/include/uapi/linux/lsm.h
index f27c9a9cc376..eeda59a77c02 100644
--- a/include/uapi/linux/lsm.h
+++ b/include/uapi/linux/lsm.h
@@ -9,6 +9,36 @@
 #ifndef _UAPI_LINUX_LSM_H
 #define _UAPI_LINUX_LSM_H
 
+#include <linux/types.h>
+#include <linux/unistd.h>
+
+/**
+ * struct lsm_ctx - LSM context information
+ * @id: the LSM id number, see LSM_ID_XXX
+ * @flags: LSM specific flags
+ * @len: length of the lsm_ctx struct, @ctx and any other data or padding
+ * @ctx_len: the size of @ctx
+ * @ctx: the LSM context value
+ *
+ * The @len field MUST be equal to the size of the lsm_ctx struct
+ * plus any additional padding and/or data placed after @ctx.
+ *
+ * In all cases @ctx_len MUST be equal to the length of @ctx.
+ * If @ctx is a string value it should be nul terminated with
+ * @ctx_len equal to `strlen(@ctx) + 1`.  Binary values are
+ * supported.
+ *
+ * The @flags and @ctx fields SHOULD only be interpreted by the
+ * LSM specified by @id; they MUST be set to zero/0 when not used.
+ */
+struct lsm_ctx {
+	__u64 id;
+	__u64 flags;
+	__u64 len;
+	__u64 ctx_len;
+	__u8 ctx[];
+};
+
 /*
  * ID tokens to identify Linux Security Modules (LSMs)
  *
@@ -51,4 +81,10 @@
 #define LSM_ATTR_PREV		104
 #define LSM_ATTR_SOCKCREATE	105
 
+/*
+ * LSM_FLAG_XXX definitions identify special handling instructions
+ * for the API.
+ */
+#define LSM_FLAG_SINGLE	0x0001
+
 #endif /* _UAPI_LINUX_LSM_H */